1. Field of the Invention
This invention is directed to test equipment, and more particularly to test equipment for circuit boards.
2. Description of the Related Art
Circuit board testers are used for testing a variety of circuit boards or similar devices to assure that the circuit boards operate as intended. In at least one type of circuit board tester, such as Agilent Model No. 3070, Series 3, a separate device, referred to as a fixture, is used to position the circuit board such that a plurality of electrically conductive probes (which are part of, or coupled to, the tester) contact predetermined components or positions of the circuit board. The particular components or positions that are contacted by the test or probes depend on the tests that are desired. When the probes are in contact with the desired locations on the circuit board, electrical signals with predetermined parameters (e.g., predetermined magnitudes or patterns of current, voltage frequency, phase and the like) are applied by the tester, typically under control of a computer, to certain of the probes. Some or all of the probes are used to measure the performance or response of the circuit board (i.e., to measure electrical parameters at some or all of the probes contacting the circuit board). In this way, it is possible to rapidly perform a number of tests or measurements characterizing the performance of the circuit board while simulating the conditions the circuit board would have, or could have, during actual use. Although it is possible to use these types of tests (and testing devices) for a variety of possible purposes (such as “spot checking” selected circuit boards at a production facility, testing circuit boards which may be malfunctioning, testing prototype circuit boards as part of a design program and the like), in at least some applications, circuit board testing is used to provide quality assurance on all or substantially all products of a given type or class which are produced by a company. Even with the relatively rapid test procedures which can be achieved by circuit testing, it is not unusual for desired testing of each circuit board to require on the order of 30 seconds to 90 seconds or more.
Because, in at least some applications, circuit board testing is performed on substantially all devices on a production line or production facility, reliability of testing can be especially important since delay or failure at a testing station can delay or interrupt the overall production in a production line or facility and cause expensive boards to be rejected. One cause of rejection or test failure is uneven or warped circuit boards.
Indeed, warped boards are quit common. The larger the board, the greater the likelihood that the board will not be sufficiently flat to conduct an accurate test. One reason why warped boards can fail a test, is that the warpage causes the probe to miss their target.
It as been assumed, that the solution to warped and uneven boards is to apply sufficient pressure on the board to even it out during test. This may work for minor warpage, but warpage of some degree will either damage the testing device by requiring so much pressure to make adequate probe contact or destroy the board. The board can be destroyed in this flattening process by snapping off surface mounted, galling the board, cracking ICs and other components, breaking leads, breaking traces or by other means which render the board unusable or untestable.
Accordingly, it would be useful to provide a fixture, useable in connection with in-circuit testers, which provides desired speed of positioning the circuit board or other unit under test (UUT) and which achieves a relatively high degree of reliability, and can test uneven boards without damage.